1. Field of the Invention
The invention relates to array microphones, and more particularly to signal delays between component microphones of an array microphone.
2. Description of the Related Art
An array microphone is a device comprising an array of microphones. Referring to FIG. 1, a block diagram of an apparatus 100 comprising an array microphone 110 is shown. When a sound propagates to the array microphone 110, each of the microphones 102 and 103 receives the same sound to respectively generate an audio signal. The array microphone 110 therefore generates a plurality of audio signals S1 and S1′ corresponding to the sound. Because the microphones have a location difference therebetween, the sound propagates to the microphones with different phases, and the audio signals S1 and S1′ have phase difference therebetween due to phase difference of received sounds. After the audio signals S1 and S1′ are amplified and converted from analog to digital to respectively obtain audio signals S3 and S3′, the digital signal processor 108 can generate an audio signal S4 reflecting a sound component coming from a specific direction according to the phase difference between the audio signals S3 and S3′.
The phase difference between the audio signals S1 and S1′ generated by the array microphone 110 are crucial for synthesis of the audio signal S4. The phase difference between the audio signals S1 and S1′ must faithfully reflect the phase difference between the sounds received by the microphones 102 and 103. When the microphones 102 and 103 generate the signals S1 and S1′ with different delay, the delay difference causes the signals S1 and S1′ to have additional phase difference therebetween, referred to as an intrinsic phase difference between the microphones 102 and 103. The intrinsic phase difference is then combined with the phase difference of the received sound to generate audio signals S1 and S1′ with the distorted phase difference, resulting in an erroneously synthesized signal S4 which cannot correctly reflect the sound component coming from the specific direction. Thus, a method for manufacturing an array microphone with smaller intrinsic phase difference between its component microphones is required.